Mail insertion machines automatically associate together, process, and place sheet articles (e.g., one or more papers, documents, or envelopes) into envelopes for mass mailing. Thereafter, a mail insertion machine can perform various other operations, such as sealing an envelope, associating stuffed envelopes with an appropriate postage weight category, and grouping or sorting by zip code or in accordance with other criteria. Mail insertion machines typically include a track to move mail pieces along an assembly line for sequential processing by one or more insert stations. Each insert station typically includes one or more hoppers, or containers, for storing sheet articles in a stack until required for processing. A single cycle of operation by an insert station usually includes removing one sheet article from the hopper via a mechanical device and subsequently stuffing the sheet article into an envelope, folding it, marking it, or otherwise preparing it for mailing.
Current mail insertion machines include a sensor to detect a low stack condition and a system for alerting an operator to a low stack condition. It is possible in mail processing for an operator to fail to replenish the sheet article stack despite receiving a low stack condition warning. Such a failure to replenish the sheet article supply can result in an unnecessary and undesirable delay in processing. Additionally, in many known insert stations, sheet articles will fall from the sheet article stack onto the track once the sheet article stack size, or level, is less than a certain size.
One known approach for alleviating these problems is to provide a first sensor for detecting when the quantity of sheet articles is below a first measured size and a second sensor for detecting when the quantity of sheet articles is below a second measured size. When the quantity is depleted until it is below the first measured size, an alert is activated to signal a low stack condition. When the quantity is depleted below the second measured size, an alert is activated to indicate the low stack condition and the insert station can be halted from pulling any more sheet articles from the stack. A disadvantage of this solution is the requirement of two sensors, thus increasing the cost of the machine.
Therefore, it is desired to improve the indication of a low stack condition. It is also desired to indicate to an operator that a sheet article stack height has fallen below a predetermined size. Furthermore, it is desired to halt the processing of any more sheet articles once the hopper has reached a second measured size without the use of a second sensor.